The invention relates generally to the measurement of an electronically transmitted signal, and more particularly to a system and method for measuring a high-speed signal, such as a signal of an integrated circuit.
After an integrated circuit (“IC”, or “chip”) has been designed and fabricated, it is tested to determine whether the chip functions as intended. As the level of integration of chips has increased, however, the difficulty of testing them has also increased.
A number of methods are used to test the operation of chips after fabrication, but many of them are ineffective to test parameters of high-speed operation. For example, in frequently used methods, a fixture having a socket outfitted with probes contacts the bond pads of a chip or a chip module. A set of signal lines connect the socket of the fixture to test equipment. When the chip or module is so connected to test equipment, basic functional operation of the chip is then verified in a sequence of tests usually lasting only seconds.
The above method is sufficient for testing many types of chips, including digital chips having outputs at speeds that match internal bus speeds of processing equipment, and analog chips having outputs at frequencies of about 300 MHz or less. However, the testing of a high-speed serial data transmitter presents challenges that cannot be satisfactorily addressed by the above method. In such testing method, the probes, socket, wiring, and printed circuit board between the chip and external test equipment have high inductance and parasitic capacitance, which limits the bandwidth of signals that can reach the test equipment. High-speed serial data transmitters produce outputs at gigahertz frequencies, some currently at 10 GHz and higher, far above the bandwidth of such fixtures and test equipment available for post-fabrication testing. Therefore, signal characteristics of the high-speed outputs cannot be measured using only the available post-fabrication test fixtures and test equipment.
Among the output signal characteristics of a serial data transmitter that are desired to be measured are rise-time, fall-time, and jitter, including the eye width and eye height of the output signal. The signal eye width represents the minimum time interval between signal transitions and the eye height represents the minimum voltage difference between high and low signal levels that is sustainable over relatively large numbers of signal cycles. Such measurements determine the quality of the transmitted output signal. An output signal having an eye width or eye height outside of tolerances can cause the bit error rate for receiving the transmitted output signal to exceed threshold.
It would be desirable to measure output signal characteristics of high-speed serial data transmitters when verifying operation of chips and modules after fabrication. However, since the output signals of such high-speed serial data transmitters are outside of the bandwidth of the available test fixtures and equipment, a new system and method are needed to measure the output signal characteristics.